I have a MBP 15 Retina Display with a Thunderbolt monitor connected to it.

I have a specific set of earphones (IEMs) which aren't being detected by the audio out port.
Despite having them plugged in I am unable to get the Thunderbolt to stop playing the sound.
The above earphones don't change the status of the Sound Pref. pane.

I have another set of earphones which are detected just fine. These do change the Sound Pref. pane to reflect headphones.

The earphones mentioned in case #1 work fine on an iPhone and don't have a Mic built-in.

How do I get the headphones to detect is there a way to force audio out of the Mac with the first earphones plugged in?